A unique TD game called "Gem Craft" its pretty good in my opinion with lots of levels, and leveling up.
When you start the game you are greeted with something that resembles this
The game plays like a normal TD in the sense that you place towers to blast creeps. But when you place towers you also have to place gems in the tower. Every time you create a gem you get a random one which you can either place in a tower, combine with another or use as ammunition with the "Gem bomb" ability
Jayisgames review: http://jayisgames.co...2008/06/gemcraft.php